We sent up up tank 5 months ago and gradually stocked it with fish then finally a pleck to clean up. We have lost 12 minnos and 6 zebra +12 other fish during this time. The only fish that has survived since the very start is a blue organa.the pleck has survived also but this was only put in the tank when advised to by the shop. The water has been cleaned regulary and treated. And the water has been checked at the shop where we purchased the fish and the equipment for ph etc and it is always given the all clear .The shop gave us the last two fish for free but they both died within a day of each other.

Can any body tell me what the problem is and why the blue organa is the only fish besides the pleck that has not died.

What size is your tank and what temperature is your water at ?
I have never heard of a blue organa , is it a goldfish type ?
What type of plec is it ? Most fish refered to as plecs are not cold water fish although they may tolerate cooler than averge tropical temps.
Zebras can be kept at lower temps than a lot of tropical species but are NOT true cold water species like gold fish.
Is the tank filtered and are you cleaning the material in it correctly - in old tank water NOT untreated tap water ?

If you can post a picture of the organa and the plec it would be useful to aid identification .

It does sound as if the aquarum shop are selling you fish that are not truely cold water species.

OP, get a book on tropical fish. Don't buy anymore fish till you have learnt how to look after them properly. Make sure you don't put TROPICAL fish into a cold water tank. Or buy a heater.

it is a 65 lit brand new coid water tank with a filter. Everything we have done is on the advise of the shop and asll the fish are from the cold water section. it wasnt purchased with the idea of kjeeping tropical fish. the blue organa and the plec which are the only surviors are both cold water type. All cleanin g methods ans solution used are as advised or proviced by the shop.

When you do water changes you should match the temperature with that of the tank.
If you are just putting in treated water straight from the cold tap (you are not using artificially softened water I hope) then it will be a good deal colder than the tank water and will chill the fish - particularly the sub tropical zebras .
Keeping a goldfish ( I think you have a blue oranda ) with much smaller fish such as white cloud mountain minnows is not recommended .
Goldfish are very tolerant of bad treatment /water conditions so I am not surprised it survived .
The minnows could have died for the reason that the tank water got too hot in the summer - my living room tanks can reach over 80 F but have tropical inhabitants so they are OK .
Lastly , do watch the number of fish in the tank at any one time .

Some fish shops are notoriously bad at giving the correct advice. If you check up on plecs (Hypostomus plecostomus.) you will find that they are tropical fish from Central and South America. They can grow up to 2 ft long. I bet the shop didn't tell you that!

Very true. Some shops only think of making money and will sell you anything. Plecs are notorious 'tank busters'. good shops will tell you they grow to really big sizes.

Are the fish coming from a specialist aquatic retailer or from a general pet store/garden centre as sometimes the staff are not as knowledgeable as they could be ?

Try this place OP.

There is also another possibility that the fish you are buying were not very healthy in the first place. That could be the fault of the shop and not yours. There are dodgy dealers out there that will palm unsuspecting customers wonky fish. The place I buy from has a return policy in that if the fish you buy from them dies within the first week they will replace it free of charge if you give them a sample of your tank water to test and it tests as safe.

I think it's more likely that a) The OP was sold tropical fish for his coldwater tank and b) he had to many fish in a 65l tank.

The shop has failed the OP big time, but I think it's the Op's responsibility to do some research on any pet he intends to keep.

I'd go along with that too.

so its a 65L tank, with numerous fish in there including a blue oranda and a plec. i would put money on the deaths being caused by an ammonia/nitrite/nitrate spike. that tank wont even hold a single oranda at adult size, and the water quality will be extremely difficult to maintain. orandas on average reach 6-8inches, but some can and do grow larger depending on water quality, genes and diet. our largest oranda is a 10inch orange and white, and our 2nd largest is a 8inch blue oranda. they need room to swim plenty too, ours use every inch of their 6ft tank the plec also is likely to cause water quality issues as they are poop machines just the same as goldies.

the danios and minnows should be fine in that tank but i would say will just about fully stock it, 65L isnt overly large, my mother in law has a 60L tank and she only has 12 small tetras and 5 cory catfish in there.

do you have a test kit? if not, its a great investment, go for a good quality liquid drop test kit such as the api master kit, which is usually around £25-£30. you need to test ammonia, nitrites and nitrates. you need to aim for ammonia 0, nitrites 0, and nitrates <40ppm which are kept low via regular weekly partial water changes and new water from the tap being treated with dechorinator before going into the tank. hope this helps a little